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Introduces animals without a backbone.

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How are these jellyfish like an insect?

Jellyfish and insects don't seem to have much in common. They look much different. They live in very different environments. But both of these animals are classified as invertebrates.

What Are Invertebrates?

Animals are also often identified as being either invertebrates or vertebrates. These are terms based on the skeletons of the animals. Vertebrates have a backbone made of bone or cartilage (cartilage is a flexible supportive tissue. You have cartilage in your ears and nose. Invertebrates, on the other hand, have no backbone (Figure below).

Snails are an example of invertebrates, animals without a backbone.

All vertebrate organisms are in the phylum Chordata. Invertebrates are divided into several phyla, some of which are listed below (Table below).

Phylum Examples
Porifera Sponges
Cnidaria Jellyfish, corals
Platyhelminthes Flatworms, tapeworms
Nematoda Nematodes, heartworm
Mollusca Snails, clams
Annelida Earthworms, leeches
Arthropoda Insects, crabs
Echinodermata Sea stars, sea urchins


  • cartilage: Firm tissue that provides flexible support in animal skeletons.
  • invertebrates: Animals that lack backbones.
  • vertebrates: Animals that have backbones of bones or cartilage.


  • Invertebrates are animals without a backbone.
  • Invertebrates include insects, earthworms, jellyfish, and many other animals.


  1. What are some examples of invertebrates?
  2. How do you determine if an animal is an invertebrate?

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